This invention relates to fasteners for clamping sheet-form members. More particularly, the invention relates to an apparatus and method for attaching an undercover onto the underside of a vehicle floor panel, in which such fasteners are inserted in mounting holes in the undercover and receive studs attached to the floor panel.
The use of fasteners for attaching a sheet-form member, such as an undercover, to a support, such as a vehicle body panel, is known. For example, studs welded to the body panel may be inserted in mounting holes in the undercover, which is secured to the body panel by threading nuts onto the studs. The studs are attached to the body panel at prescribed intervals and positions, but a certain range of allowable error in the positioning of the studs is allowed. In Japanese Unexamined Utility Model Application No. S62-73109/1987 (Gazette), a member to be mounted is not specified as being an undercover, but apparatus is described in which fasteners are secured to the member and are fastened to studs of a support, such as a panel to which the studs have been secured. Such apparatus can be used for attaching an undercover to a panel to which studs have been secured, but no consideration is given to the allowable error referred to above.
When nuts are tightly screwed onto studs to attach an undercover to a body panel, tightening stress is concentrated in the undercover at the fastening positions. Undercovers made of plastic are placed in a high-temperature environment, heated when the vehicle engine is running, cooled when the engine stops running, and are expanded and contracted by temperature changes.
When the undercover is strongly fastened by nuts screwed onto studs, there is a danger of plastic deformation of the undercover at the fastening positions. It is desirable to maintain secure attachment for the undercover and yet to accommodate expansion and contraction in the plane of the undercover due to temperature changes, so as to prevent deformation.
U.S. Pat. Nos. 6,824,203 and 7,036,875, both incorporated herein by reference, disclose an apparatus and method for attaching an undercover onto the underside of a vehicle floor panel in a simple manner that allows movement of the undercover along the plane of the undercover, in the direction of expansion and contraction, to accommodate temperature changes, while preventing play in the direction of a stud axis, to maintain secure attachment of the undercover to the floor panel. Tubular fasteners are used that comprise first and second clips with flanges for clamping the undercover between them with a prescribed clamping force. The tubular fasteners are inserted in mounting holes of the undercover with diametral clearance, and the prescribed clamping force allows movement of the undercover in the planar direction but prevents movement perpendicular to the planar direction.
While the inventions disclosed in the aforesaid U.S. patents provide a solution to the plastic deformation problem, there is the potential for loosening of the connection of the fasteners to the studs due to unintended turning of a first clip of a fastener relative to a second clip of the fastener, caused by vibration, for example.